Sensitive data such as keys for operating systems and programs, passwords, and the like can be written to a hard disk drive for subsequent access to, e.g., programs and data on the HDD. The present invention critically recognizes that it is important that once written, secure data should be rendered difficult to copy or modify. Otherwise, a hacker might, e.g., modify a password that he cannot read into one that he can, and then use the modified password to access data that is supposed to be protected. Or, the hacker might copy secure data to another device for later decoding of the data at a convenient time and place. With this recognition in mind, the invention below provides tamper-resistant data.